This invention relates to new Power Factor Correction (PFC) alternating current/direct current (AC/DC) power supplies and more particularly to those power supplies in which the energy transfers directly from the input line to the output during any period that the input line voltage exceeds a preset value and this invention claims the benefit of priority from United States Provisional Application Serial No. 60/308,740 filed Jul. 30, 2001.
A number of national and international standards require that the harmonics of the line current of electronic equipments be limited to certain specified levels. The typical prior art approaches for meeting these requirements are set forth in the patent literature as follows:
U.S. Pat. No. 5,434,767 to Batarseh, et al.; U.S. Pat. No. 5,636,106 to Batarseh, et al.; U.S. Pat. No. 5,844,787 to Fraidlin, et al.; U.S. Pat. No. 6,266,256 to Lehnert, et al.; and, U.S. Pat. No. 6,044,002 to Van Der Wal, et al., however, each are without an additional winding connected to the rectified input side and not arranged to transfer energy to the output directly during the time when the line voltage exceeds a preset value.
Additional background art includes: U.S. Pat. No. 5,508,903 to Alexndrov, et al.; U.S. Pat. No. 5,903,446 to Huillet, et al.; and, U.S. Pat. No. 6,097,614 to Jain, et al. which are each to a DC/DC cell (not for a PFC AC/DC cell); and, U.S. Pat. No. 6,046,914 to Lauter which uses the additional winding connected with the Boost inductor as a voltage feedback sensor to alleviate the voltage across the bulk capacitor.
Thus, it appears from the prior art teachings known to the inventors that the approaches for meeting the harmonics requirements of the line current are either:
1) to add a power factor corrector ahead of the isolated direct current/direct current (DC/DC) cell section of the switching mode power supply (Two-Stage Scheme); or,
2) integrate the function of power factor correction and isolated DC/DC conversion into a single power stage (One-Stage Scheme).
Unfortunately, both of these prior art approaches are characterized by a major disadvantage in that they have inherent low efficiency due to the fact that energy is processed twice during its transferring process. This results in very high switching losses in the main switch.
It is an important object of this invention to provide a new energy transfer concept to improve the efficiency of power factor correction AC/DC cells.
It is a further object of this invention to reduce the high switching losses of the main switch.
According to the invention, there is a power factor cell constructed ahead of the current-fed DC/DC conversion cell, and an additional winding coupled to the DC/DC transformer is connected to the rectified input side and arranged to transfer energy to the output directly during the line voltage exceeds preset value. Therefore, the efficiency of the cell can be improved considerably due to the reduced power processing time.
According to the invention, the power factor cell can operate both in continuous current mode (CCM) or discontinuous current mode (DCM). The power factor correction cell and current-fed DC/DC cell cell can share a common switch with single control loop or use different switches with separate control loops.